In an interview in the wake of a two-day visit to Turkey last week, Rehn said that difficulties in Turkey’s EU membership talks would not be brushed aside in order to avoid a clash of civilisations.

Turkey faces suspension of accession talks later this year if it fails to open its ports and airports to Cypriot flag carriers.

“In Turkey the politicians and citizens tend to overestimate the strategic importance of Turkey to Europe, we should try and balance this,” he said.

“Turkey should not overplay its card and think that it can have some kind of saving or bargain of the conditions for enlargement because it is of strategic importance.”

In an interview with ­European Voice in September, Ali Babacan, Turkey’s chief negotiator with the EU, said that the derailment of talks on EU membership would damage ­Europe’s ­image in the ­Middle East and its relations with the Muslim world.

But Rehn admitted that while many in Turkey overestimated the country’s role as a bridge between Europe and the Muslim world, many in Europe did not fully appreciate the geopolitical importance of Turkey.

“In the EU, political leaders and citizens underestimate the importance of Turkey both in terms of our strategic ­interest in the Middle East and in terms of being a bridge between civilisations, between Europe and Islam.”

He said that relations between the EU and Turkey had not been helped by a spate of ­comments from EU ­politicians calling for a pause to EU enlargement, or a privileged partnership with Turkey, instead of full membership.

“There is quite some bubbling in the chemistry between the European Union and Turkey for the moment…we are not yet at the brink of an ­explosion and I trust we can avoid that, but this current bubbling is often caused by misunderstanding,” said Rehn.

“The sometimes constant questioning of the accession perspective of those countries to whom we have provided an ­accession perspective tends to erode our own credibility and the credibility of our conditionality.

“Both the candidate country and the European Union are suffering from this constant existential debate.”

Ahead of a Commission report on Turkey’s progress toward joining the EU, to be published on 8 November, Rehn warned that Ankara will have to reform a controversial law on ­“insulting Turkishness”.

“It [the law] is against the most fundamental ­European principles of freedom of expression,” he said. “It has been my ­request to either repeal or amend [it] so that it will be brought into line with the European Convention on Human Rights.”

The Turkish government has so far been reluc­tant to change article 301 of the penal code, ­under which writers such as Orhan Pamuk and Elif Shafak faced charges for insulting Turkishness (Shafak was subsequently acquitted and the charges against Pamuk were dropped). It has asked the EU to wait and see how the law is ­being implemented.

But during what he ­described as “intense ­exchanges” in Turkey last week, Rehn said he had made it clear that the EU could not wait.

“Even if the evolving ­jurisprudence would, in some years, take care of the problem it…would take too long and the whole process would run out of steam, we cannot afford to wait five years.

“Freedom of expression is not an alternative to the fight against terrorism.”

But the commissioner pointed out that there was a perception in Turkey “that the European Union has not shown solidarity towards Turkey, by disregarding the terrorist ­attacks in Turkey while underlining and condemning the attacks in Madrid and London”.

“They have a point,” added Rehn.

Despite the controversy over article 301, the major obstacle to Turkey cont­inuing talks with the EU ­appears to be the diploma­tic deadlock over Cyprus.

The EU’s demand that Turkey open its ports and airports to Cypriot flag carriers has so far been met by counter demands from Turkey that the EU resume direct trade with northern Cyprus.

Turkey now faces the partial suspension of talks if progress is not made.

Rehn said that the consequences of not reaching a deal on Cyprus before the end of the year would be catastrophic and would result in years of delay.

He urged all EU member states to focus their efforts on reaching a deal.

“The alternative to plan A, that we succeed, call it plan B or whatever, is in any case so dark and negative that I would not want to concentrate on any of these matters.”

Although details of a possible deal have not been made public, Rehn confirmed that the United Nations might play a substantial role in starting EU trade with northern Cyprus.

“The UN is willing to contribute and assist the European Union regarding its task of implementing the trade regulation. At the same time the UN very well realises the sense of urgency.”

It is rumoured that the UN could take control of the port of Famagusta, ­allowing trade to begin, in return for the Turkish Army handing over control of the ghost town of Varosha.